1. Field of the Invention
The present invention relates to tools and methods for disposing, coating, repairing, or otherwise modifying the surface of a metal substrate using frictional heating and compressive/shear loading of a consumable metal against the substrate. More particularly, embodiments of the invention include friction-based fabrication tooling comprising a non-consumable member with a throat and a consumable member disposed in the throat, wherein consumable filler material is capable of being introduced to the throat in a continuous manner during deposition using frictional heating and compressive/shear loading of the filler material onto the substrate.
2. Description of Related Art
Conventional coating techniques, such as flame spray, high-velocity oxygen fuel (HVOF), detonation-gun (D-Gun), wire arc and plasma deposition, produce coatings that have considerable porosity, significant oxide content and discrete interfaces between the coating and substrate. Typically, these coating processes operate at relatively high temperatures and melt/oxidize the material as it is deposited onto the substrate. Such conventional techniques are not suitable for processing many types of substrates and coating materials, such as nanocrystalline materials due to the grain growth and loss of strength resulting from the relatively high processing temperatures.
An alternative deposition process available is referred to as cold spray type depositing. Such techniques typically involve a relatively low-temperature thermal spray process in which particles are accelerated through a supersonic nozzle. These techniques, however, may be relatively expensive and/or generally incapable of processing high aspect ratio particles, such as nanocrystalline aluminum powder produced by cryomilling. As a result, products prepared using cold spray techniques typically contain oxide impurities.
In light of these drawbacks, the inventors have developed new coating deposition techniques by having designed various friction-based fabrication tools capable of depositing coatings on substrates efficiently and in a simple manner. For example, the inventors have developed a tool comprising a non-consumable body and a throat defining a passageway lengthwise through the body, which are shaped to deliver a consumable material to a substrate and form a coating on the substrate using compressive loading and frictional heating. Such tools are capable of resulting in high quality adhesions between the substrate and coating and high strength products having an increased resistance to failure. In addition, the inventors have developed tools having internal tool geometry and means for exerting normal forces on the consumable during rotation to further enhance the tool's capability of delivering or depositing the feed material to or on the substrate.
The inventors have made further advancements in this field by reducing the effect of some of the mechanical challenges presented by feeding solid material into a spindle, including reducing down time of the machinery due to build up of consumable material within the spindle, improving efficiency of the deposition process by finding ways to continuously introduce consumable material to the tool, and by developing processes for introducing variations in the composition of the feed material during the deposition process for preparing functionally graded substrates in a simplified manner.
Such advancements in the coating field have made digital manufacturing by friction stir fabrication of specialty alloys a possibility. State-of-the-art digital manufacturing technologies for metal parts have evolved around powder metallurgy and fusion welding-based processes. Both of these processing methodologies yield parts with inferior mechanical and physical properties as compared to wrought metal of the same composition. Additionally, the production rates for even the fastest processes are relatively low (˜40 lbs/hr for Ti) and the part envelopes are limited to a few cubic feet.
To address some of these particular manufacturing difficulties, the present inventors have proposed a novel high-speed, large-volume wrought metal deposition technology capable of enabling affordable, full-density, near net-shape component manufacturing from a wide range of alloys, including specialty high-strength steels and ultra fine-grained alloys. The ability to rapidly fabricate complex wrought alloy components from the ground up will provide a leap-ahead advancement in digital manufacturing and combat readiness.